The use of different techniques for controlled moving or deflection in free space of electromagnetic radiation, such as a microwave signal or an optical frequency signal, are well known in the art for various applications.
At present, said deflection techniques are, for example, widely used in optical radar or microwave radar, in space or military applications, optical commutation devices, surveillance systems, etc.
Optical beam deflection techniques using electro-mechanical means which comprise movable mechanical parts for controlled deflection of an optical beam or signal are known. For example, deflection arrangements including electrically controlled rotating mirrors are known in the art.
In some cases the use of deflection instruments with movable mechanical parts is expensive, while in other cases it can be inefficient and give rise to problems. For example, one problem connected to the use of said instruments is caused by the fact that their performance, in some cases, can be significantly influenced by vibrations to which these instruments are subjected. Typically, this can take place when said instruments are intended to be installed on vehicles such as automobiles or aircraft to be used, for example, as radar system transmitting antennas.
Another problem connected to the use of instruments with movable parts can be caused by their dimensions, in some cases incompatible with the dimensions laid down by specific applications. Furthermore, the beam deflection speed is limited by the performance of the mechanical system.
In order to overcome the above-mentioned problems and disadvantages, techniques using systems known as Phased Array Systems have been widely used for some time. Said techniques were originally developed for applications using microwave signals and, subsequently, they were further extended to the field of optical frequency signals.
Using said technologies, it is possible to move or deflect into free space an optical signal or a microwave signal, by making a plurality of signals emitted from respective radiating elements interfere with each other and varying and controlling the reciprocal phase differences between said emitted signals.
Controlled variation of phase differences between signals is obtained typically by varying respectively the dielectric constant or the refractive index of the means through which the microwave or optical signals respectively are propagated.
A particular example of a phased array beam scanning antenna for a microwave car radar is described in the U.S. Pat. No. 6,587,076.
Despite the fact that the phased array technology is now consolidated in applications using microwave signals, the use of said technology still presents some problems in applications using optical frequencies. Said problems are mainly connected to the typical dimensions of the circuits using optical signals. In fact, said dimensions are strictly connected to the wavelengths of the optical signals which are much smaller than the characteristic wavelengths of microwave signals. Accurate control of the dimensions of the optical paths is indispensable for accurate control of the phase differences.
An example of a device suitable to deflect an optical beam based on the phased array technology is described in U.S. Pat. No. 5,233,673.
In said document, a deflectable optical beam is obtained by controlled interference between a plurality of signals emitted from a respective plurality of optical emitters supplied by respective optical guides and arranged along a linear axis. The principle of the control method is based on the piezoelectric effect or the electro-optical effect. However, control is complicated and insufficient since it has to control a number of phase differences between signals proportional to the number of optical emitters used. Furthermore, another problem left unresolved by the above-mentioned U.S. Pat. No. 5,233,673 is that of a possible undesired coupling between the optical guides.